First, According to the Marine Times, there will be several changes to the rifle. Such changes include,
- RCO reticles replaced with SDO(Squad Day Optic) used on the M27 IAR
- Free-floating barrel
- Ambidextrous charging handles
- Better trigger
- Modern flash hider
- Better ammunition(AB49 Special Operations Science and Technology 5.56mm cartridge)
There will be some considerations for placement of holsters and ammunition for pistols
On similar note, Glock 19 has been authorized for MARSOC as USSOCOM asset. The pistols will be considered as USSOCOM inventory, not MARSOC's but MARSOC can qualify with it.
You can read more about it from the Soldier Systems Daily
http://soldiersystems.net/2015/02/17/marsoc-authorized-to-use-glock-19s/
From: Military Times, Soldier Systems Daily
